1. Field of the Invention
This invention relates to the structure of an auto-return type push switch.
2. Description of the Prior Art
FIGS. 3 and 4 are explanatory drawings of a conventional push switch.
In FIG. 4, reference numeral 1 designates a casing made of insulating material, 2 designates a cylindrical hole with a bottom formed in the upper surface of the casing 1, 3 designates a U-shaped groove formed at a portion of the periphery of the cylindrical hole 2, and 4 designates a spring bearing erected on the bottom surface of the casing 1 adjacent to the inner periphery of the cylindrical hole 2. In this spring bearing 4 is embedded a fixed electrode 5, this fixed electrode 5 being led out of the casing 1 via a terminal 6 embedded in the bottom of the casing 1 as shown in FIG. 3. 7 designates a helical spring accommodated in the cylindrical hole 2 with its portion fitted in a gap 8 between the spring bearing 4 and the inner periphery of the cylindrical hole 2, which is configured so that as a lower end portion of the spring 7 is placed on another fixed electrode 9 embedded in the bottom surface of the casing 1 this spring 7 is kept in contact with the fixed electrode 9. 9a designates a lead terminal of the fixed electrode 9. 10 designates a slide member, and 11 designates a clip-shaped movable contact segment which is accommodated in a groove 13 formed in a movable contact segment accommodating portion 12 of the slide member 10. This accommodating portion 12 is loosely fitted in the helical spring 7. A colllar 14 provided above the accommodating portion 12 is engaged with an upper end portion of the helical spring 7. 10a designates a projection portion provided at a portion of the slide member 10 for guiding the slide member 10 when moving.
One end of the helical spring 7 is fixed to an attaching portion 15 of the movable contact segment 11 through, for example, a welding process, and the movable contact segment 11 is in contact with both surfaces of the fixed electrode 5. 16 designates a cover plate whose upper surface is provided with a collar 17 in relation to the cylindrical hole 2 of the casing 1. A lug 19 of the slide member 10 projects outside the cover plate 16 through a hole 18 formed in the collar 17. The cover plate 16 is secured to the casing 1 by coupling holes 21 formed in attaching legs 20 of the cover plate 16 with projections 22 provided on the external surface of the casing 1.
According to the conventional push switch of the foregoing structure, as the lug 19 being in the non-pushed state of FIG. 3 is pushed downward or toward the bottom of the drawing, the slide member 10 moves down while the projection portion 10a is being guided by the groove 3 of the casing 1, and the collar 14 of the slide member 10 compresses the helical spring 7. During the above pushing action the movable contact segment 11 slides on from a non-conductor portion 24 to a conductor portion 25 of the fixed electrode 5, as a result, the fixed electrode 5 comes into conduction with the other fixed electrode 9 via the movable contact segment 11 and the helical spring 7, and the contacts of the switch assume the ON state. If the pushing force is removed, owing to the resiliency of the helical spring 7 the lug 19 returns to its initial non-pushed state shown in FIG. 3.
The foregoing switch, however, has the following problems:
(1) A welding process or a soldering process is necessary to secure one end of the helical spring 7 to the attaching portion 15 of the movable contact segment 11, thus, the efficiency of assembly work is low,
(2) The helical spring 7 must have a low resistance because it is used as a part of the contact, thus, the spring 7 must be silver-plated, thereby resulting in a high cost, and
(3) Contact between the helical spring 7 and the fixed electrode 9 is realized in a mode of point contact, thus is unstable and gives a large contact resistance.